Nano-Recycling?

Another news piece that appeared in the November 2013 issue of Materials Today. I was very impressed by this paper (reference at the end) so hope that the news piece does it justice!

Turning Plastic Bags into Carbon Nanotubes

The University of Adelaide have developed a process for transforming waste plastic bags into well-organised carbon nanotube membranes.

We all try to reuse and recycle the plastic bags we get from supermarkets, but some Australian researchers have gone one high-tech step further – a team from the University of Adelaide have used these non-degradable bags to produce carbon nanotubes (CNTs), and they hope that this discovery will help develop the next generation of advanced filtration materials.

Most current approaches to CNT synthesis rely on expensive carbon precursors such as methane, and iron- or cobalt-based catalysts. But this work, published in Carbon, is based on a catalyst- and solvent-free chemical vapour deposition (CVD) approach for producing CNT-alumina membranes, using commercially available supermarket plastic bags as the carbon source.

The Adelaide team, led by Prof. Dusan Losic, was driven by the need to find a method of cheaply producing large quantities of high-quality CNTs. And by using a waste material as the source of carbon, they may also have found a way to recycle the countless plastic bags thrown away every year. In their system, small squares (1 cm2) of linear low-density polyethylene (LLDPE) bags are thermally decomposed. Under an inert atmosphere, the carbon from the LLDPE is deposited in the form of CNTs within templates of nanoporous anodic alumina membranes (NAAMs).

NAAMs feature hexagonally arranged nanopores that cut through the membrane, allowing the team to control the geometry and orientation of the CNTs, without the need for a catalyst. The surface chemistry of the CNTs could also be controlled by further functionalization stages. The team showed that these CNTs membranes (CNT-NAAMs) could be precisely engineered to recognise particular molecules, and so, could be used as low-dimensional high-efficiency filters in separation applications (e.g. desalination of water). These membranes could also be recycled by thermal cleaning and/or sonication.

The individual CNTs produced by this technique were multi-walled, could be reputably produced, and compared favourably with those synthesised by other methods. And unlike traditional catalyst-based CVD techniques, the geometry of the CNTs produced by Losic and his team could be tightly controlled.

Producing carbon nanotube membranes in this way offers a scalable way to synthesise CNTs, while reducing the use of poisonous compounds, and may lead to a new breed of filtration materials. Nanotechnological recycling of your shopping bags may be only a few years away.

Carbon (2013) doi:10.1016/j.carbon.2013.07.003